Laser doping techniques for high-efficiency crystalline semiconductor solar cells

Abstract

Various laser processing schemes are disclosed for producing various types of hetero-junction and homo-junction solar cells. The methods include base and emitter contact opening, selective doping, metal ablation, annealing to improve passivation, and selective emitter doping via laser heating of aluminum. Also, laser processing schemes are disclosed that are suitable for selective amorphous silicon ablation and selective doping for hetero-junction solar cells. Laser ablation techniques are disclosed that leave the underlying silicon substantially undamaged. These laser processing techniques may be applied to semiconductor substrates, including crystalline silicon substrates, and further including crystalline silicon substrates which are manufactured either through wire saw wafering methods or via epitaxial deposition processes, or other cleavage techniques such as ion implantation and heating, that are either planar or textured/three-dimensional. These techniques are highly suited to thin crystalline semiconductor, including thin crystalline silicon films.

1 . A method for doping a solar cell substrate, said method comprising:
 providing a semiconductor substrate;   depositing a passivation layer on a surface of said semiconductor substrate, said passivation layer comprising a predetermined quantity of dopant, said dopant comprising either a p-type dopant or an n-type dopant;   selectively heating said passivation layer via laser irradiation, said selective heating causing said dopant to diffuse into said semiconductor substrate, said diffused dopant creating either a doped surface field or doped emitter region in said semiconductor substrate.   
     
     
         2 . The method of  claim 1 , wherein said selective heating further causes improved surface and bulk passivation of said semiconductor substrate. 
     
     
         3 . The method of  claim 1 , wherein said semiconductor substrate comprises an epitaxial thin film substrate having a thickness approximately in the range of 5 to 100 microns. 
     
     
         4 . The method of  claim 1 , wherein said semiconductor comprises silicon. 
     
     
         5 . The method of  claim 4 , wherein said semiconductor comprises monocrystalline silicon. 
     
     
         6 . The method of  claim 4 , wherein said semiconductor comprises multi-crystalline silicon. 
     
     
         7 . The method of  claim 1 , wherein said doped passivation layer comprises a substance chosen from the group consisting of silicon nitride, silicon oxynitride, silicon oxide, silicon-rich silicon nitride, silicon-rich silicon oxide, and the dopant comprises phosphorous. 
     
     
         8 . The method of  claim 1 , wherein said doped passivation layer comprises a doped amorphous silicon/silicon nitride stack, and said dopant comprises phosphorous. 
     
     
         9 . The method of  claim 1 , wherein said laser comprises either a continuous wave laser or a pulsed laser having a pulse length greater than approximately 10 nanoseconds. 
     
     
         10 . The method of  claim 1 , wherein said laser comprises a wavelength of approximately 10.6 micrometers or less. 
     
     
         11 . The method of  claim 3 , wherein said epitaxial film is supported on a substrate. 
     
     
         12 . The method of  claim 11 , wherein said substrate is suitable for processing temperatures up to approximately 300° C. 
     
     
         13 . The method of  claim 11 , wherein said substrate is suitable for processing temperatures up to approximately 400° C. 
     
     
         14 . The method of  claim 1 , wherein said step of depositing a passivation layer takes place at a temperature approximately in the range of 90° C. to 400° C. 
     
     
         15 . The method of  claim 1 , wherein said laser heating is substantially limited to a depth of approximately 20 microns or less. 
     
     
         16 . The method of  claim 15 , wherein said laser comprises a pulsed laser of wavelength less than approximately 828 nanometers. 
     
     
         17 . The method of  claim 8 , wherein said laser annealing is carried out such that said amorphous silicon crystallizes into monocrystalline silicon by epitaxy. 
     
     
         18 . The method of  claim 1 , further used to form front surface field in an all back contact, back junction solar cell. 
     
     
         19 . The method of  claim 3 , wherein said epitaxial film comprises three-dimensional pyramids or prisms formed via a textured template liftoff process. 
     
     
         20 . The method of  claim 3 , wherein said epitaxial film comprises a substantially planar semiconductor layer formed via an epitaxial silicon liftoff process. 
     
     
         21 . A method for doping a solar cell substrate, said method comprising:
 providing a semiconductor substrate having n-type doping;   depositing a borosilicate glass layer on a surface of said semiconductor substrate, said borosilicate glass layer comprising a predetermined quantity of boron dopant;   selectively heating said borosilicate glass layer via laser irradiation, said selective heating causing said dopant to diffuse into said semiconductor substrate, said diffused dopant creating an emitter region in said semiconductor substrate.   
     
     
         22 . A method for doping a front contact solar cell substrate, said method comprising:
 providing a semiconductor substrate comprising p-type doping;   depositing a borosilicate glass layer on a surface of said semiconductor substrate, said borosilicate glass layer comprising a predetermined quantity of boron dopant;   selectively heating said borosilicate glass layer via laser irradiation, said selective heating causing said dopant to diffuse into said semiconductor substrate, said diffused dopant creating a surface field in said semiconductor substrate.